1. Field of the Invention
The present invention relates to a spatial light modulation device using a hologram lens layer and a color display apparatus using the spatial light modulation device.
2. Description of the Related Art
In a color display apparatus, color filters are necessary constituent elements. A conventional color filter is constituted by a resin layer which uses a pigment or dye as a coloring material and selectively transmit only one of the wavelength bands corresponding to R (red), G (green), and B (blue) which are the three primary colors of light. However, the conventional color filters corresponding RGB are formed in independent regions, respectively. A light ray which can be transmitted through the filter in each region is only one light ray of only one color of RGB in incident white light, and other light rays are absorbed by the filter. When a pixel size decreases, the filters of the color light rays are formed such that the filters partially overlap at boundary portions of the regions. For this reason, black stripes are generally formed on the boundary portions of adjacent regions to avoid color mixture. Therefore, a light transmittance of all the color filters is low, an efficiency of using light cannot be theoretically improved. The absorbed light rays are converted into heat, and the heat may be a factor in degrading display characteristics.
In contrast to this, in recent years, use of color filters (to be referred to as hologram color filters hereinafter) using hologram lenses is studied. According to the hologram color filters, by the diffraction and spectral functions of hologram lenses, white light can be diffracted and dispersed into three light components, i.e., RGB. Since use of such a hologram color filter can obtain a high efficiency of using light, the hologram color filter is effective to a projection type liquid-crystal display apparatus which requires improvement of an efficiency of using light.
FIG. 1 is a device sectional view showing a typical structure of a spatial light modulation device in a projection type color liquid-crystal display apparatus having a reflection scheme disclosed in Publication of Patent Applications (Japanese Unexamined Patent Publication No. 9-189809) filed by the present applicant. In this spatial light modulation device, as a color filter, the hologram color filter described above is used as a color filter. In FIG. 1, reference numeral 11 denotes a liquid crystal panel; 12, a thin-plate glass layer; 13, a color filter; 14, a glass substrate; and 15, a coupling prism.
The liquid-crystal panel 11 has a structure in which a silicon substrate 21; an active matrix drive circuit 22 formed on the silicon substrate 21; a pixel electrode layer 23 obtained by regularly arraying pixel electrodes 23r, 23g, and 23b selectively controlled and driven by the active matrix drive circuit 22; a dielectric mirror film 24, an alignment film 25, a light modulation layer 26 having a liquid crystal sealed by a spacer; an alignment film 27; and a transparent common electrode layer 28 are sequentially laminated.
The color filter 13 is constituted by a so-called hologram lens array in which unit hologram lenses are regularly arrayed. The color filter 13 has a function of diffracting and dispersing read light (white light) including three primary colors, i.e., R, G, and B in units of color light rays to almost perpendicularly converge the light rays to the positions of the pixel electrodes 23r, 23g, and 23b corresponding to R, G, and B in the liquid-crystal panel 11. More specifically, main beams of beams are almost perpendicularly incident on the pixel electrodes 23r, 23g, and 23b, and the beams can be converged on the pixel electrodes 23r, 23g, and 23b by the lens functions thereof. Therefore, the projection type color liquid-crystal display apparatus using incident light without waste can be provided. As shown in FIG. 1, when the dielectric mirror film 24 is arranged on the pixel electrode layer 23, the destination of convergence is the dielectric mirror film 24.
FIG. 2 a diagram showing a color separation theory of read light (white light) of a hologram color filter in the spatial light modulation device shown in FIG. 1. As shown in FIG. 2, the color filter 13 has an arrangement in which a hologram color filter layer 13r for R, a hologram color filter layer 13g for G, and a hologram color filter layer 13b for b which correspond to the three primary colors, i.e., RGB are laminated. Of white light which is admitted on the color filter 13 at a predetermined angle, light rays having corresponding wavelengths are diffracted and dispersed by these layers, respectively.
For example, an R light component is diffracted and dispersed by the first layer 13r, a G light component is diffracted and dispersed by the second layer 13g, and a B light component is diffracted and dispersed by the third layer 13b. The R, G, and B light rays dispersed and diffracted by the layers are substantially converged on the corresponding pixel electrodes 23b, 23g, and 23r.
In this manner, a spatial light modulation device using conventional hologram lenses must comprise hologram lens layers corresponding to light colors of the three primary colors, i.e., RGB. More specifically, the hologram lens layers of a three-layer structure. Therefore, in the steps in manufacturing the hologram lens layers, hologram lens layers of three types must be manufactured. In addition, when the three layers are laminated, the positions of the three layers must be aligned with high precision such that light rays diffracted and dispersed by the hologram lens layers are converged on corresponding pixel electrodes, respectively.
For this reason, processes are cumbersome, process costs increase, and a high-definition color liquid-crystal display apparatus cannot be easily manufactured because of a problem in alignment precision.